Estrogen-stimulated progesterone synthesis by slices of rabbit corpora lutea has been previously demonstrated in our laboratory. The current project was designed to identify the step(s) in the steroidogenic pathway influenced by estrogen. Luteal tissue from pregnant rabbits (Day 11) will be incubated with estradiol-17B and/or designated treatment compounds for 3 or 8 hours. Initial experiments utilizing labelled precursors and metabolic inhibitors (AY-9944, aminoglutethimide phosphate, oxymethylone)will be carried out to determine the possible site(s) of estradiols control of progesterone production. Additional experiments will be conducted to characterize the site and mechanism of action by assaying estradiol influenced enzyme activity. This unique system, found only in the rabbit, offers an excellent opportunity to contrast the "luteotropic" mechanism of estrogen with that of LH, thus yielding greater insight into the intricate mechanism of corpus lutem function.